Laying hens from 2 lines, selected for high and low residual component of feed intake in the laying period, (R+ and R- respectively) were distributed in 2 groups (high/low ingestion of crude proteins) receiving rations of the same level in energy and non-proteinic essential components. The content of the rations in total protein was calculated according to the feed intake of the 2 lines so as to provide these lines with nearly the same daily amount of protein within each experimental group. A higher daily protein intake causes a higher body weight, mean egg weight, shell percentage and plasma uric acid level and a lower residual feed consumption and weight of gizzard as percent of body weight. The difference between the R+ and R- lines is highly significant not only for feed intake, its residual component and feed efficiency of egg production, but also for age at first egg, percent of shell-less, double-yolked and cracked eggs, yolk weight, adult body weight, feathers and gizzard in percent of live weight, which are higher in the R+ line, and for weight and percentage of shell in the egg, which are superior in R-. These differences are consistent with previous observations. The feed intake of the 2 lines and its residual component remain considerably different irrespective of the level of protein intake; however, the lower protein supply is associated with a lower feed intake, body weight and laying rate for the R+ but not for the R- layers (significant line x treatment interactions). Although these lines differ for their feed and energy intake at any protein level, it is likely that the R+ line uses more protein than R- for energy production.
